Method of forming heterogeneous photoconductive compositions and elements

ABSTRACT

A METHOD OF FORMING HETEROGENEOUS PHOTOCONDUCTIVE COMPOSITIONS COMPRISES THE STEPS OF FORMING A FIRST SOLUTION OF A CARBONATE POLYMER AND A PYRYLIUM DYE, SUBJECTING THE SOLUTION TO SHEARING ACTION, PREPARING A SECOND SOLUTION OF PYRYLIUM DYE ALONE AND COMBING THE FIRST AND SECOND SOLUTIONS WITH AN ORGANIC PHOTOCONDUCTOR AND A POLYMERIC BINDER DIFFERENT FROM THE CARBONATE POLYMER, COATING THE RESULTANT COMBINATION AND DRYING.

United States Patent 3 679,407 METHOD OF FORMING HETEROGENEOUS PHOTOCONDUCTIVE COMPOSITIONS AND ELEMENTS Curtis L. Stephens, Brockport, N.Y., assignor to Eastman Kodak Company, Rochester, NY.

No Drawing. Filed Nov. 13, 1970, Ser. No. 89,447

Int. Cl. G03g 5/00 U.S. Cl. 96--1.6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to electrophotography and to photoconductive elements and structures useful in electrophotography. in addition, this invention relates to methods for preparing electrophotographic elements.

Electrophotographic imaging processes and techniques have been extensively described in both the patent and other literature.

Generally, these processes have in common the steps of employing a normally insulating photoconductive element which is prepared to respond to imagewise exposure with electromagnetic radiation by forming a latent electrostatic charge image. A variety of subsequent operations, now well known in the art, can then be employed to produce a permanent record of the image.

One type of photoconductive insulating structure or element particularly useful in electrophotography utilizes a composition containing a photoconductive insulating material dispersed in a resinous material. A unitary electrophotographic element is generally produced in a multilayer type of structure by coating a layer of the photoconductive composition onto a film support previously overcoated with a layer of conducting material or the photoconductive composition may be coated directly onto a conducting support of metal or other suitable conducting material. Such photoconductive compositions have shown improved speed and/or spectral response, as well as other desired electophotographic characteristics when one or more photosensitizing materials or addenda are incorporated into the photoconductive composition. Typical addenda of this latter type are disclosed in U.S. Patent Nos. 3,250,615, issued May 10, 1966, by VanAllan; 3,141,770,

issued July 21, 1964, by Davis et al.; and 2,987,395, issued 1 June 6, 1961, by Jarvis. Generally, photosensitizing addenda to photoconductive compositions are incorporated to effect a change in the sensitivity or speed of a particular photoconductor system and/or a change in its spectral response characteristics. Such addenda can enhance the sensitivity of an element to radiation at a particular wavelength or to a broad range of wavelengths where desired. The mechanism of such sensitization is presently not fully understood. The phenomenon, however, is extremely useful. The importance of such effects is evidenced by the extensive search currently conducted by workers in the art for compositions and compounds which are capable of photosensitizing photoconductive compositions in the manner described.

Usually, the desirability of a change in electrophotographic properties is dictated by the end use contemplated for the photoconductive element. For example, in docu- "ice ment copying applications, the spectral electrophotographic response of the photoconductor should be capable of reproducing the wide range of colors which are normally encountered in such use. If the response of the photoconductor falls short of these design criteria, it is highly desirable if the spectral response of the composition can be altered by the addition of photosensitizing addenda to the composition. Likewise, various applications specifically require other characteristics such as the ability of the element to accept a high surface potential, and exhibit a low dark decay of electrical charge. It is also desirable for the photoconductive element to exhibit high speed as measured in an electrical speed or characteristic curve, a low residual potential after exposure and resistance to fatigue. Sensitization of many photoconductive compositions by the addition of certain dyes selected from the large number of dyes presently known has hitherto been widely used to provide for the desired flexibility in the design of photoconductive elements in particular photoconductor-containing systems. Conventional dye addenda to photoconductor compositions have generally shown only a limited capability for over-all improvement in the totality of electrophotographic properties which cooperate to produce a useful electrophotographic element or structure. The art is still searching for improvements in shoulder and toe speeds, improved solid area reproduction characteristics, rapid recovery and useful electrophotographic speed from either positive or negative electrostatic charging.

A high speed heterogeneous or aggregate photoconductive system was developed by William A. Light which overcomes many of the problems of the prior art. This aggregate composition is the subject matter of copending application Ser. No. 804,266, filed Mar. 4, 1969', now U.S. Patent No. 3,615,414, and entitled Novel Photoconductive Compositions and Elements. The addenda disclosed therein are responsible for the exhibition of desirable electrophotographic properties in photoconductive elements prepared therewith. However, in accordance with the procedures described therein, the preparation of electrophotographic elements uses a solvent treatment step subsequent to the coating step. In an effort to avoid this secondary treatment step, a novel method of preparation of photoconductive compositions of the type described by Light is disclosed in copending Eugene P. Gramza application Ser. No. 821,513, filed May 2, 1969, now U.S. Patent NO. 3,615,415, and entitled Method for the Preparation of Photoconductive Compositions. This latter method involves the high speed shearing of the photoconductive composition prior to coating and thus eliminates subsequent solvent treatment.

An additional problem encountered in forming such heterogeneous photoconductive compositions is that many of the dyes useful in preparing such compositions have several crystalline structures. Depending upon which crystalline structure of the dye is present when using the above techniques, the formation of the aggregate compositions can be relatively easy or quite difiicult. In an effort to avoid the diificulties often encountered with different crystalline structure, a novel dye-first proce dure is used as described in copending Eugene P. Gramza et al. application Ser. No. 816,831, filed Apr. 16, 1969, now U.S. Patent No. 3,615,396 and entitled Method for the Preparation of Photoconductive Compositions.

All of the techniques described above are useful. However, these methods do not provide wide flexibility in the choice of binder since the aggregate is typically formed and used in one binder. Accordingly, there is a need for a method of obtaining aggregate photoconductive compositions containing a variety of binders in a single formulation.

It is, 'therefore, an object of this invention to provide the art of electrography with a novel method of preparing aggregate photoconductive compositions.

It is an additional object of this invention to provide a method for the in situ formation of aggregate photoconductive compositions containing a mixture of two or more polymeric materials.

It is a further object to provide a method of preparing aggregate-containing elcctrophotographic elements.

These and other objects and advantages of the invention will become apparent from the following description of the invention.

In accordance with the present invention, a first solution is formed of a dye and polymer. This solution is subjected to high speed shearing. A second solution is prepared which contains only dye. After the dye is thoroughly dissolved in the second solution, it is combined with both the first solution and a combination of a 7 photoconductor and a polymeric binder different from the polymer in the first solution. The combination is mixed, coated and dried to form a heterogeneous photoconductive composition containing a discontinuous phase comprised of a combination of dye and polymer which combination has a wavelength range of absorption different than the wavelength range of absorption of a substantially homogeneous combination of the dye and polymer.

The method of this invention is used to form aggregate compositions contained in a 'variety of hinders, the aggregate being of the type originally disclosed in the abovementioned application to W. A. Light. The present method is relatively simple and allows the formation of aggregate photoconductive compositions in situ with 'various binders. After formation of the combination of materials referred to above, it is typically coated on a suitable support which results in the formationof a separately identifiable multiphase composition, the heterogeneous nature I of which is generally apparent when viewed, for example, under 2500 magnification, although such compositions may appear to be substantially optically clear to the naked eye in the absence of magnification. There can, of course, be macroscopic heterogeneity. Suitably, the dyecontaining-aggregate in the discontinuous phase is predominantly in the size range of from about 0.01 to about 10.0 microns. However, it should be noted that when the heterogeneous compositions of the invention are used to sensitize a particulate photoconductor, such as zinc oxide, another discontinuous phase will be present which may not fall within this size range.

In general,the heterogeneous compositions formed by the present method are multiphase organic solids. The

polymer binder which is added to the first and second solutions forms an amorphous matrix or continuous phase which contains a discrete discontinuous phase as distinguished from a solution. The discontinuous phase is the aggregate species which is a co-crystalline complex comprised or the dye and polymer of the first and second solutions. The term co-crystalline complex as used herein has reference to a crystalline compound which contains dye and polymer molecules co-crystallized in a single crystalline structure to form a regular array of the molecules in a three dimensional pattern.

When the present method is used to prepare heterogeneous compositions containing organic photoconductors, the resultant compositions generally contain only two phases as the photoconductor usually forms a solid solution with thercontinuous phase of polymeric binder. On the other hand, when the present method is used with particulate photoconductors, such as zinc oxide, three phases are present. In such a case, there would be a continuous phase of polymeric binder, a discontinuous phase containing the aggregate as discussed above and another discontinuous phase comprised of the particulate photo- "conductor. Of course, the present multiphase compositionsmay also contain additional discontinuous phases of '4 trapped impurities, etc. Another feature characteristic of the heterogeneous compositions formed in accordance with this invention is that the wavelength of the radiation absorption maximum characteristic of such compositions is substantially shifted from the wavelength of the radiation absorption maximum of a substantially homogeneous dye-polymer solid solution formed of similar constituents. The new absorption maximum characteristic of the aggregates formed by this method is not necessarily an overall maximum for this system as this will depend upon the relative amount of dye in the aggregate. Such an absorption maximum shift in the formation of multiphase heterogeneous systems for the present invention is generally of the magnitude of at least about 10 e um. If mixtures of dyes are used, one dye may cause an absorption maximum shift to a long wavelength and another dye cause an absorption maximum to a shorter wavelength. In such cases, a formation of the heterogenerous compositions can more easily be identified by viewing under magnification.

Sensitizing dyes and electrically insulating polymeric materials are used in forming the aggregate compositions. Typically, pyrylium dyes, including pyrylium, thiapyrylium and selenapyrylium dye salts are useful in forming such compositions. Such dyes include those which can be represented by the following general formula:

wherein R, R R, R and R can each represent (a) a hydrogen atom; (b) an alkyl group typically having from 1 to 15 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl, amyl, isoamyl, hexyl, octyl, nonyl, dodecyl, etc., (c) alkoxy groups like methoxy, ethoxy, propoxy, butoxy, amyloxy, hexoxy, octoxy, and the like; and (d) aryl groups including substituted aryl groups such as phenyl, 4-diphenyl, alkylphenyls as 4-ethylphenyl, 4-propylphenyl, and the like, alkoxyphenyls as 4-ethoxyphenyl, 4-methoxyphenyl, 4-amyloxyphenyl, 2-hexoxyphenyl, 2-methoxyphenyl, 3,4-dimethoxyphenyl, and the like, fi-hydroxy alkoxyphenyls as 2-hydroxyethoxyphenyl, 3-hydroxyethoxypheny-l, and the like, 4-hydroxyphenyl, halophenyls as 2,4-dichlorophenyl, 3,4-dibromophenyl, 4- chlorophenyl, 3,4-dichlorophenyl, and the like, azidophenyl, nitrophenyl, aminophenyls as 4-diethylaminophenyl, 4- dimethylaminophenyl and the like, naphthyl; and vinyl substituted aryl groups such as styryl, methoxystyryl, diethoxystyryl, dimethylaminostyryl, 1-butyl-4-p-dimethylaminophenyl-1,3-butadienyl, fl-ethyl 4 dimethylaminostyryl, and the like; and where X is a sulfur, oxygen or selenium atom, and Z- is an anionic function, including such anions as perchlorate, fiuoroborate, iodide, chloride,

members of such pyrylium dyes are listed in Table 1.

TABLE 1 Compound number Name of compound 1 4-[4-bis-(2-chloroethyl)aminophenyl]-2,6-diphenylthiapyrylium perchlorate.

2 l-(fdimethylaminophenyl)-2,6-dipheuylthiapyrylium perchlorate.

3 4-(4-dimethy1aminophonyl)-2,6-diphenylthlapyrylium fluoroborate.

4 4-(4-dimetl1ylami110-2-methylphenyl) -2,6-dlphollylpyrylium perchlorate.

5 4-[4-bis(2-chloroethy1)aminopheny1l-2-(-methoxyphenyl)-6-pheny1thiapyrylium perchlorate.

6 4-(4 ilfimethylaminophenyl)-2,6diphenylthiapyrylium su a a.

7 4-(4-dimethylaminophenyl)-2,6-diphenylthiapyrylium p-toluenesulfonate.

S -1-(44limethy1aminopl1enyl)-2,6-diphenylpyrylium p-toluenesulfonate.

useful are those linear polymers, including copolymers, containing the following moiety in the recurring unit:

wherein:

R and R when taken separately, can each be a hydrogen atom, an alkyl radical such as methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, and the like including substituted alkyl radicals such as trifluoromethyl, etc., and an aryl radical such as phenyl and naphthyl, including substituted aryl radicals having such substituents as a halogen, alkyl radicals of from 1 to 5 carbon atoms, etc.; and R and R when taken together, can represent the carbon atoms necessary to form a cyclic hydrocarbon radical including cycloalkanes such as cyclohexyl and polycycloalkanes such as norbornyl, the total number of carbon atoms in R and R being up to 19;

R, and R can each be hydrogen, an alkyl radical of from 1 to 5 carbon atoms or a halogen such as chloro, bromo, iodo, etc.; and

. R, is a divalent radical selected from the following:

Preferred polymers useful in the present method of forming aggregate crystals are hydrophobic carbonate polymers comprised of the following recurring unit:

wherein Each R is a phenylene radical including halo-substituted phenylene radicals and alkyl-substituted phenylene radicals; and R and R are as described above. Such compositions are disclosed, for example, in US. Pat. 'Nos. 3,028,365 by Schnell et al., issued Apr. 3, 1962 and 3,317,- 466 by Caldwell et al., issued May 2, 1967. Preferably polycarbonates containing an al'kylidene diarylene moiety in the recurring unit such as those prepared with Bisphenol A and including polymeric products of ester exchange between diphenylcarbonate and 2,2-bis (4-hydroxyphenyl) propane are useful in the practice of this invention. Such compositions are disclosed in the following US. patents: 2,999,750 by Miller et al., issued Sept. 12, 1961; 3,038,- 874 by Iaakso et al., issued June 12, .1962; 3,038,879 by Laa kso et al., issued June 12, 1962; 3,038,880 by Laakso et al., issued June 12, 1962; 3,106,544 by laa'kso et al.,

issued Oct. 8, 1963; 3,106,545 by Laakso et al., issued Oct. 8, 1963; and 3,106,546 by Laalrso et al., issued Oct. 8, 1963. A wide range of film-forming polycarbonate resins are useful, with completely satisfactory results being obtained when using commercial polymeric materials 'which are characterized by an inherent viscosity of about 0.5 to about 1.8.

The following polymers are included among the materials useful in the practice of this invention:

TABLE 2 Number Polymeric material 1 Poly(4,4-isopropylidenediphenylene-co-l,koyclohexyldimethylcarbonate). 2 Poly(3,sethylenedioxyphenylene thiocarbonate). 3 Poly(4,4-isopropylidenediphenylene carbonate-coterephthalate) Poly (4,4-isopropyliden ediphenylene carbonate).

. Poly(4,4'-isopropylidenediphenylene thiocarbonate).

Poly(2,2-butanebis4-phenylene carbonate).

7 Poly (4,4-isopropylidenediphenylene carbonate-blockethylene oxide).

8..-..- Poly (4,4-isopropylidenediphenylene carbonate-blocktetramethyleneoxide) 9..-. Poly[4,4-isopropylidenebis(2-methylphenylene)carbonate].

l0 Poly(4,4-isopropylidenediphenylene-co-l,4-phenylene carbonate).

11 Poly(4, -isopropy1idenediphenylene-co-l,3-phenyleno carbonat 12 Poly (4, tisgpropylidenediphenylene-co-4,4' diphenyleue 27 Poly 2,2-(4-methylpentane)bis-4-phenylene carbonate].

28 Polyf4,4-(2-norbornylidene) diphenylene carbonate].

29 Poly,4-(hexahydro-4,7-methanoindan-5-ylidene)- diphenylene carbonate].

30 Poly(4,4-isopropylidenediphenylene carbonate-blockoxytetramethylene) The aggregate crystals formed according to the present invention can readily be used for enhancing the sensitivity and extending the spectral range of sensitivity of a variety of organic photoconductors and inorganic photoconductors including both nand p-type photoconductors. A typical example of an inorganic photoconductor would be zinc oxide. The present invention can be used in connection with many organic, including organo-metallic, photoconducting materials which have little or substantially no persistence of photoconductivity. Representative organometallic compounds are the organic derivatives ofGroup HIa, Na, and Va metals such as those having at least one amino-aryl group attached to the metal atom. Exemplary organo-metallic compounds are the triphenyl-p-dialkylaminophenyl derivatives of silicon, germanium, tin and lead, the tri-p-dialkylaminophenyl derivatives of arsenic, antimony, phosphorus, bismuth boron, aluminum, gallium, thallium and indium. Useful photoconductors of this type are described in copending Goldman and Johnson US. patent application Ser. No. 650,664, filed July 3, 1967 and Johnson application Ser. No. 755,711, filed Aug. 27, 1968.

An especially useful classof organic photoconductors is referred to herein as organic amine photoconductors.

Such organic photoconductors have as a common structural feature at least one amino group. Useful organic photoconductors which can be spectrally sensitized in accordance with this invention include, therefore, arylamine compounds comprising (1) diarylamines such as diphenylamine, dinaphthylamine, N,N-diphenylbenzidine, N-phenyl-l-naphthylamine, N-phenyl-2-naphthylamine, N,N'-diphenyl-p-phenylenediamine, 2 carboxy-5-chloro-4'-methoxydiphenylamine, p-anilinophenol, N,N-di-2-naphthylp-phenylenediamine, those described in Fox US. Patent 3,240,597, issued Mar. 15, 1966, and the like, and (2) triarylamines including (a) nonpolymeric triarylamines, such as triphenylamine, N,N,N',N' tetraphenyl-m-phenylenediamine, 4 acetyltriphenylamine, 4 hexanoyltriphenylamine, 4 lauroyltriphenylamine, 4 hexyltriphenylamine, 4 dodecyltriphenylamine, 4,4 bis(diphenylamino)benzil, 4,4 bis(diphenylamiuo)benzophenone and the lkie, and (b) polymeric triarylamines such as poly [N,4" (N,N',N' triphenylbenzidine)], polyadipyltriphenylamine, polysebacyltriphenylamine, polydecamethylenetriphenylamine, poly-N (4-vinylphenyl)diphenylamine, poly-N-(vinylphenyl) a,u'-dinaphthylamine and the like. Other useful amine-type photoconductors are disclosed in US. Patent 3,180,730, issued Apr. 27, 1965.

Useful photoconductive substances capable of being sensitized in accordance with this invention are disclosed in Fox US. Patent 3,265,496, issued Aug. 9, 1966, and include those represented by the following general forwherein T represents a mononuclear or polynuclear divalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, binaphthyl, etc.), or a substituted divalent aromatic radical of these types wherein said substituent can comprise a member such as an acyl group having from 1 to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from 1 to about 6 carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy, etc.), or a nitro group; M represents a mononuclear or polyunclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), or a substituted monovalent aromatic radical wherein said substituent can comprise a member, such as an acyl group having from 1 to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from 1 to about 6 carbon atoms (e.g., methoxy, propxy, pentoxy, etc.), or a nitro group; Q can represent a hydrogne atom, a halogen atom, or an aromatic amino group, such as MNH-; b represents an integer from 1 to about 12; and R represents a hydrogen atom, a mononuclear or polynuclear aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), a substituted aromatic radical wherein said substituent comprises an alkyl group, an alkoxy group, an acyl group, or a nitro group, or a poly(4-vinylphenyl) group which is bonded to the nitrogen atom by a carbon atom of the phenyl group.

Polyarylalkane photoconductors are particularly useful in producing the present invention. Such photoconductors are described in US. Patent 3,274,000 by Noe et al., issued Sept. 20, 1966, French Patent 1,383,461 and in copending application of Seus and Goldman, titled Photoconductive Elements Containing Organic Photoconductors, Ser. No. 627,857, filed Apr. 3, 1967. These photoconductors include leuco bases of diaryl or triaryl methane dye salts, 1,1,1-triarylalkanes wherein the alkane moiety has at least two carbon atoms and tetraarylmethanes, there being substituted an amine group on at least one of the aryl groups attached to the alkane and methane moieties of the latter two classes of photoconductors which are non-leuco base materials.

Preferred polyarylalkane photoconductors can be represented by the formula:

wherein each of D, E and G is an aryl group and I. is a hydrogen atom, an alkyl group, or an aryl group, at least one of D, E and G containing an amino substituent. The aryl groups attached to the central carbon atom are preferably phenyl groups, although naphthyl groups can also be used. Such aryl groups can contains such substituents as alkyl and alkoxy typically having 1 to 8 carbon atoms, hydroxy, halogen, etc., in the ortho, meta or para posi- 10 tions, ortho-substituted phenyl being preferred. The aryl groups can also be joined together or cyclized to form a fluorene moiety, for example. The amino substituent can be represented by the formula:

wherein L can be an alkyl group typically having 1 to 8 carbon atoms, a hydrogen atom, an aryl group, or together the necessary atoms to form a heterocyclic amino group typically having 5 to 6 atoms in the ring such as morpholino, piperidino, tetrahydropyrrole, etc. At least one of D, E, and G is preferably p-dialkylaminophenyl group. When I is an alkyl group, such an alkyl group more generally has 1 to 7 carbon atoms.

Representative useful polyarylalkane photoconductors include the compounds listed in Table 3.

TABLE 3 Compound number Name of compound 1 4,4-benzylidene bis(N,Ndiethyl-rn-toluidine) 2 4',4-diamino--dimethylarnino-Z,2-

dimethyltriphenylmethane.

3 4,4-bis(diethylamino)-2,6-dichl0ro-2',2-

dimethyltripheny]methane.

4 4,4-bis(diethyla.mino)-2,2"-

d1methyldiphenylnaphthylmethaue.

5 2,2"-dimet.hyl-4,4,4-

tr-is(dimethylamino)triphenylmethane.

(i 4 ,4"-bis( liethylamino)-4-dimethylamino-2,2-

dimethyltriphenylmethane.

7 4 ,4 -bis(diethy1amino) -2-ehloro-2 ,2 -dimethyl-idimethylaminotriphenylmethane.

8 4,4-bis(diethylamino)-4-dimethylarnino-2,2,2-

trimethyltriphenylmethane.

9 4,4"-bis(dimethylamino) -2-chloro2,2-

dimethyltriphenylmethane.

10 4,4-bis(dirnethylamino) -2 ,2 -dimethyl-4- methoxytriphenylmethane.

11 Bis(4-diethy1ami no) -1 ,1 ,l-triphenylethane.

12 Bis(i-diethylamino)tetraphenylmethane.

l3 4,4-bis(benzylethylamino)-2,2-

dimethyltriphenylmethaue.

14 4,4-bis(diethylamino)-2,2-diethoxy triphenylmethane.

15 4,4-bis(dimethylarnino) -1,1 ,l-triphenylethane.

16 1-(4N,N-dimethylaminophenyl)-1,l-diphenylethane.

17 -dimethylaminotetraphenylmethane.

18 4-diethylaminotetraphenylmethane.

Another class of photoconductors useful in this invention are the 4-diarylamino-substituted chalcones. Typical compounds of this type are low molecular weight nonpolymeric ketones having the general formula:

where R and R are each aryl radicals, aliphatic residues of 1 to 12 carbon atoms such as alkyl radicals preferably having 1 to 4 carbon atoms or hydrogen. Particularly advantageous results are obtained when R is a phenyl radical including substituted phenyl radicals and where R is diphenylaminophenyl, dimethylaminophenyl or phenyl.

Other photoconductors which can be used with the present aggregate compositions include rhodamine B, malachite green, crystal violet, phenosafranine, cadmium sulfide, cadmium selenide, parachloronil, benzil, trinitrofluorenone, tetranitrofluorenone, etc.

In preparing the photoconductive compositions in accordance with this invention, useful results are obtained when an organic, including organo-metallic, photoconductor is present in an amount equal to at least about Vz by weight of total solids added to the coating solvent.

The upper limit of the amount of photoconductor present can be varied widely with up to 99% by weight of total solids being useful. A preferred weight range for the photoconductor is from about 10 to about 80 weight percent. Of course, if it is desired to use the present aggregate compositions alone as the photoconductive substane, then no photoconductor would be added. In addition to the photoconductors described above, polymeric photoconductors can also be used if desired.

The polymeric binders useful in the present invention include a wide variety of polymeric materials which can be hydrophobic or hydrophilic. Suitable binders must be sufficiently electrically insulating so as to prevent destruction of any electrostatic charge pattern formed on the resultant electrophotographic elements. The particular polymeric binder material used is not critical provided it is a film-forming organic polymer which is electrically insulating as mentioned above and is not reactive to the other ingredients. Additionally, the polymeric binder used is typically different from the polymer in the first solution referred to previously in that the polymer of the first solution is actually entering into the formation of the aggregate while the polymeric binder serves as a matrix in which the aggregate is dispersed. The polymeric binder vehicle can be comprised of a mixture of materials. In

particular, it can be comprised of an amount of a polymer similar to that in the first solution together with one or more polymers entirely distinct from that of the first solution. Useful polymeric binder vehicles include the representative materials listed in Table 4 below, as well as mixtures of these polymers alone or with the polymer of the first solution.

In addition to the polymeric materials referred to above, the polymeric binder can also be a polymeric photoconductor such as the various photoconductive carbazole polymers, including the halogenated po1y(vinyl carbamoles). In such a case, there would be no need for the separate addition of another photoconductor; however, one could be added if so desired. Also, a polymeric photoconductor could be used in conjunction with a compatible polymeric binder.

Solvents useful in preparing the first and second solutions, containing respectively, dye and polymer, and dye alone, include a variety of organic liquids. Useful solvents would include various ketones'such as dialkyl ketones having from 1 to about 3 carbon atoms in the alkyl moiety such as dimethyl ketone, methyl ethyl ketone, etc.; aromatic hydrocarbon solvents such as benzene including substituted benzene compounds, e.g., toluene; chlorinated hydrocarbon solvents such as dichloroalkanes having 1 to about 3 carbon atoms, e.g., methylene chloride, ethylene chloride, trimethylene chloride; ethers, such as tetrahyw .drofuran, etc.; and mixtures of these and other solvents.

As mentioned above, a first solution is prepared and subjected to high speed shearing. This solution is formed .by adding a pyrylium dye and a carbonate polymer, for

example, to a suitable solvent for both components. The dye concentration is generally within the range of about 0.5 to about 20%, based on the weight of polymer and preferably is about 1 to about 4%. The polymer concentration is typically in the range of about 5 to about 20% .of the solution and preferably from about to about bient room temperature with no external heating or cool- 7 ing means. However, in order to insure uniformity, it is usually preferred that the solution be maintained at a relatively constant temperature throughout the shearing step. This can be accomplished through the use of separate heating or cooling means. Typically, the temperature maintained during shearing is in the range of about 0 to about 50 C.

In addition to the first solution, a second solution is also prepared. This second solution contains only dye dissolved in a suitable solvent compatible with the solvents of the first solution. The dye contained in this second solution is a pyryliumtype dye as described above, but may be different from the dye of the first solution. The dyes in the two solutions can, of course, be identical. The conditions of dissolution of the dye in the second solution are not critical, e.g., the temperature can range from about 0 to about 50 C., of course, decomposition temperatures and freezing temperatures should generally be avoided. Preferably, the dye is substantially completely dissolved prior to use of this solution. The concentration oggye this solution is typically from about 0.1 to about 1 g./

After the dye is dissolved in the second solution, it is combined with both the first solution and the photoconductor and polymeric binder material. The photoconductor and binder are dissolved in the solvents of the first and second solutions. This combination may also contain minor amounts of various coating aids, plasticizers, etc. The photoconductor, binder vehicle and first and second solutions are combined with stirring to insure thorough mixing. This addition step is most conveniently carried out at ambient conditions; however, the temperature can range from about 0 to about 50 C.

The coating compositions so produced typically have a total solids content (amount of material added to solvent) of about 2.5 to about 40% by weight. The total amount of dye is usually about 0.10 to about 10.0% by weight with about .25 to about 5.0% being preferred. The polymer which combines with the dye to form the aggregate is typically present in the coating dope in an amount ranging from about 0.5 to about 30% and preferably about 1.0 to about 15% by weight of the coating composition.

The resultant coating dope is then coated onto a suitable support. Coating thicknesses of the photoconductive composition on the support can vary widely. Normally, a coating in the range of about 2.5 microns to about 300 microns before drying is useful for the practice of this invention. The preferred range of coating thickness is found to be in the range from about 50 microns to about microns before drying, although useful results can be obtained outside of this range. The resultant dry thickness of the coating is preferably between about 2 microns and about 50 microns, although useful results can be obtained with a dry coating thickness between about 1 and about 200 microns.

The conditions under which the coating is prepared depend upon the nature of the solvent or solvents used, the nature and amount of the second vehicle and the thickness of the desired coating. Useful coating temperatures range from 0 C. to 50 C. with 15 to 30 C. being preferred. Useful solvent exhaust conditions vary from no external draft to that in which a high draft (high volume of air flow across coating block) is maintained.

Suitable supporting materials upon which photoconductive layers are coated according to the method of this invention can include any of a wide variety of electrically conducting supports, for example, paper (at a relative humidity above 20 percent); aluminum-paper laminates; metal foils such as aluminum foil, zinc foil, etc.; metal 13 plates, such as aluminum, copper, zinc, brass and galvanized plates; vapor deposited metal layers such as silver, nickel, aluminum, and the like coated on paper or conventional photographic film bases such as cellulose acetate, polystyrene, etc. Such conducting materials as nickel can be vacuum deposited on transparent film supports in sufficiently thin layers to allow electrophotographic elements prepared therewith to be exposed from either side of such elements. An especially useful conducting support can be prepared by coating a support material such as poly(ethylene terephthalate) with a conducting layer containing a semiconductor dispersed in a resin. Such conducting layers both with and without insulating barrier layers are described in US. Patent 3,245,833 by Trevoy, issued Apr. 12, 1966. Likewise, a suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride and a vinyl acetate polymer. Such kinds of conducting layers and methods for their optimum preparation and use are disclosed in US. 3,007,901 by Minsk, issued Nov. 7, 1961, and 3,262,807 by Sterman et al., issued July 26, 1966.

The method of this invention allows the formation of the prescent aggregate photoconductive compositions in a variety of binders. Consequently, there is greater flexibility in the type of electrophotographic elements which can be produced. This method is particularly useful in that it readily allows the formation of photoconductive compositions containing a binder which is or 'can be readily rendered hydrophilic. This has particular application in the formation of elements useful as lithographic printing masters. That is, the freedom of choice of binder, which the present method affords, allows one to'choose a suitable binder on the basis of its hydrophobic-hydrophilic properties. Thus, hydrolyzable cellulose acetate, for example, can be used as the binder. Such 'an element can be charged, imagewise exposed and then developed wlth a hydrophobic toner. After fixing the toner, the developed element is subjected to an alkaline bath to render hydrophilic the areas carrying no toner. This results in a lithographic plate which is ready to be wetted and inked for use.

Other advantages also gained by the greater flexibility which the present invention affords in the selection of binders. For example, binders can be chosen which by themselves may not form the present aggregate photoconductive composition, but which have'other desired physical properties. Thus, binders can be chosen for their adhesion properties with adjacent layers. Similarly, binders can be chosen for their leach resistance. That is, binders can be chosen, which have a greater resistance to the solvent leaching of sensitive species contained therein during liquid development and cleaning of the element.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 A solution of 0.08 gram of Dye 1, 3.96 grams of Lexan 145 polymer and 28.6 ml .of methylene chloride solvent is placed in a high-speed shearing blender and subfiected to high-speed shearing for 30 minutes at a temperature of about 20 C. Dye 1 is 4-(4-dimethylaminophenyl)-2,6- diphenylthiapyrylium perchlorate. Lexan 145 is a trademark for a bisphenol A polycarbonate resin of General Electric Company. Next, a 0.06 g. portion of Dye 1 is dissolved in 6.0 ml. of methylene chloride to form a second solution. Two ml. of the first solution and all of the second solution are added to a combination of 0.6 g. of binder and 0.4 g. of photoconductor. This procedure is repeated three times using as the photoconductor, 4,4- benzylidene-bis (N,N diethyl-m-toluidine (Photoconductor I) with the following binders: Binder 1 is Vitel PElOl which is a trademark for a polyester of Goodyear Tire and Rubber Co., believed to be poly(4,4'-isopropylidenebisphenoxyethl-co-ethylene terephthalate) 50/50; Binder 2 is Koppers 8X polystyrene resin; and Binder 3 is polyvinyl-m-bromobenzoate-co-vinylacetate. Each of the resultant formulations is coated at a 0.004 inch wet thickness on a poly(ethylene terephthalate) film support having coated thereon a 0.4 neutral density nickel conducting layer. The spectrophotometric properties of each of the resultant elements is measured after drying and each is found to have a 686 nm. wavelength of maximum absorption. Cross-section photomicrographs of each element indicate the presence of a heterogeneous phase. Each element is then electrostatically charged under a corona source until the surface potential, as measured by an electrometer probe, reaches about 600 volts. The chaged element is then exposed to a 3000 K. tungsten light source through a stepped density gray scale. The exposure causes reduction of the surface potential of the element under each step of the gray scale from its initial potential, V to some lower potential, V, the exact value of which depends upon the actual amount of exposure in meter-candle-s'econds received by the area. The results of these measurements are then plotted on a graph of surface potential V vs. log exposure for each step. The actual positive or negative speed of the photoconductive composition can then be expressed in terms of the reciprocal of the exposure required to reduce the surface potential to any fixed, arbitrarily selected value. Herein, unless otherwise stated, the actual positive or negative speed is the numerical expression of 104 divided by the exposure in meter-candle-seconds required to reduce the 600 volt charged surface potential to a value of 500 volts (shoulder speed) or to 100 volts (toe speed). The results of these speed measurements are shown in Table 5 below:

TABLE 5.ELECTRICAL SPEEDS Positive Negative Shoulder Toe Shoulder Toe Element Binder speed speed speed speed EXAMPLE 2.

A first solution is prepared and sheared as in Example 1 with the exception that 0.08 gram of Dye II is used. Dye II is 4 (4-dimethylaminophenyl)-2,6-diphenylthiapyrylium fluoroborate. Two coating formulations are prepared as in Example 1 using the presheared first solution containing Dye H and Lexan and a second solution of Dye II only. These two formulations contain difierent concentrations of Binder 1. In addition, a control formulation is made which contains no Binder 1. The resultant formulations are then coated as described in Example 1. The resultant elements each show a shift in maximum absorption to 686 nm. In addition, cross-section photomicrographs of these elements indicate that all contain a heterogeneous phase. The three formulations contain the following ingredients:

a As in formulation except Lexan 145 in 'Next, each of the elements are measured for electrophotographic speed as in Example '1. The results of these measurementsare shown below;

The above data indicate that significant improvements can be made in the electrophotographic' speed with negative charging as the layer thickness is increased in a com- The electrophotographic elements prepared by formulations 2 and 3 show improvement in negative speeds over that of the control. New formulations 1, 2 and 3 are again prepared as above and coated onto a poly(ethylene terephthalate) base containing a conductive coating prepared from the sodium salt of the carboxyester lactone of maleic anhydride in a vinyl acetate polymer, as disclosed I in Example 5 of US. Pat. No. 3,262,807 by Sterman etaI., issued July 26, 1966. The elements prepared from formulations 2 and 3 exhibit good adhesion to this con ductive underlayer; whereas, the element. prepared with formulation 1 (control) exhibited poor adhesion to this same layer.

1 7 EXAMPLE 3 The following formulations are prepared in accordance with the procedure of Example 2:

Formulation Ingredients Amount, g.

Binder 1 Photoconductor I Dye Methylene chloride Lexan/Dye II sheared solutio Binder 1 Bis(4-diethylamino)tetraphenyl methane (photoconduetor II).

ye II Methylene chloride Lexan/Dye II sheared solution Binder 1 Tris(4-N N-diethylamino-2-methylphenyllmethane (photoconduetor III). Dye II Methylene chloride 1 Lexan/Dye II sheared solution l 7 As in formulation 4 except Lexan 145 in place of binder 1.

place of binder 1. 9 As in-formulation 6 except Lexan 145 in place of binder 1.

' Each of the'above formulations is coated on a poly(ethyl- 'eneterephthalate) film base having a 0.4 density nickel ference filter having 20% transmittance for wavelengths greater than'600 nm. The electrical photographic speeds are measured as described in Example 1 for the elements which have a varying thickness of the photoconductive composition. The results of these measurements are shown I in Table 6 below:

position made according to the present invention'as opposed to a similar element carrying a composition con taining only the aggregate-forming polymer alone as the sole binder. The mixed polymeric vehicle aggregate systems formedby the present invention exhibit higher negative electrophotographic speeds with increasing layer thickness; whereas, single vehicle aggregate systems show decreasing negative speeds with increasing layer thickness.

EXAMPLE 4 The first solution is prepared by the high-speed shearing for one-half hour of 15.6 grams of Lexan 145, 0.32 gram of 4 -(4-dimethylaminophenyl)-2,6-diphenylthia- ,pyrylium fluoroborate (Dye II) and 107.20 ml. of dichloromethane solvent. Next, a second solution is prepared by stirring 0.24 gram of Dye II and ml. of dichloromethane forabout 2 /2 hours. Four ml. of the first sheared solution and all of the second solution are added to 4.24 grams of cellulose triacetate polymeric grams of 4,4-diethylamino-2,2'-dimetliyltriphenylmethanev photoconduetor is added with additional stirring for one-half hour. The resultant formulation is then coated at a.0.004 inch wet thickness on a 0.004 inch thick poly (ethylene terephthalate) film support. having coated thereon an evaporated nickel conducting layer. .After drying, the resultant electrophotographic element is charged in the dark to approximately a negative 600 volt surface potential by subjecting it to a corona charger. The element is then imagewise exposed using a tungsten light source and developed by magnetic brush developing technique using a toner material comprising a carbonate resin binder and carbon black. The developed element was then heated to about 120 C. for a few seconds to fuse the image thereon. The element is then immersed for 60 seconds in an alkaline bath containing 5.0 grams ofsodium hydroxide dissolved in grams of a 50:50 water ethanol mixture. The element is removed and rinsed in water and allowed to dry. Theresultant element is then wetted with a fountain solution formed of 3M Fountain concentrate for paper master diluted 1:7 and then inked with Van Son 40904 printers ink. It is noted that the areas of the element bearing fused toner material attracted the printers ink while the un-. covered photoconductive surface was found to be oleo-' phobic and repelled ink. Theresulting printing plate is placed on a press (Whitin Masterlith) andused to pre- I pare prints on paper. A good quality image is obtained with no apparent scumming (no ink buildup in background, hydrolyzed areas) or other degradation of image quality after 250 prints are prepared. The ink-water differential exhibited by this plate is excellent and does not appear to change significantly during the entire run.

EXAMPLE 5 The general procedure of Example 2 is repeated in forming a sheared solution of Dye II and Lexan 145. Portions of this first solution are then used, together with a second solution comprised of Dye II dissolved in methylene chloride, to prepare several coating formulations. In addition to thefirst and second solutions,

- 17 photoconductor I and a variety of binders are used. The various formulations contain the following:

The resulting formulations were coated on a conducting support as in Example 3 to form electrophotographic elements. These elements are each measured for electrophotographic speed as in the preceding examples. The results of these measurements are as follows:

ELECTRICAL SPEEDS Positive Negative Formulation Binder Shoulder Toe Shoulder Toe number number speed speed speed speed Table 7 below gives the composition of the various binders.

TABLE 7 Binder number Composition 4 Pr l ytginyl-vinylidene chloride (Geon 222, Goodrich rubber 0. 5 Terpolyrner of polyvinyl bntyrlvinyl acetate-vinyl alcohol (Butvnr 13-76, Monsanto Chemical (30.).

6 Chlorinated polyethylene (65.8% CI) (Texan Eastman 00.). 7 Polyurethane (Estane X-150, Goodrich Rubber 00.). 8 Polyvinyl toluene-styrene copolymer (Piecotex 120, Penn- Industrial Chemical 00.). 9 Chlorinated polyvinyl chloride (60% Cl) (Rhenoflex 63,

Rhelnfelder 00.).

It should be apparent that the high speed shearing referred to herein can be efiectively accomplished by a variety of shearing mechanisms. Many commercially available high-speed shearing devices are well suited for use in the practice of the present invention and exemplary devices are sold under such trade names as Gaulin Homogem'zer, Cowles Dissolver, Premier Mill Dispersator, etc. The effectiveness of any device selected may be easily ascertained without undue experimentation by preparing sample coatings as described herein and inspecting the coatings for the formation of the feature compositions. Electrophotographic data will also help in determining the optimum combinations of conditions necessary to obtain the results desired.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be elfected within the spirit and scope of the invention.

I claim:

1. A method of forming a heterogeneous photoconductive composition comprising the steps of preparing a first solution of about 5 to about 20% of a carbonate polymer and about 0.5 to about 20% based on the weight of the polymer of a pyrylium dye, subjecting said solution to shearing for an interval of time at least about 10 minutes, preparing a second solution of pyrylium dye alone in a concentration of about 0.1 to about 100 g./l., adding said sheared first solution and said second solution to a combination of an organic photoconductor and a polymeric binder different from said carbonate polymer, mixing, coating the resultant composition and drying to form a heterogeneous photoconductive composition having a discountinuous phase containing a combination of said dye and carbonate polymer and having a wavelength range of absorption ditferent than the wavelength range of radiation of a substantially homogenenous combination of said dye and polymer.

2. The method as described in claim 1, wherein the dye is selected from the group consisting of a pyrylium and thiapyrylium dye salt.

3. The method as described in claim 1 wherein the dye is a 2,4,6-triphenylthiapyrylium dye salt.

4. The method as described in claim 1 wherein the solvent for said second solution is a halogenated hydrocarbon.

5. A method of forming a heterogeneous photoconductive composition comprising the steps of preparing a first solution of a pyrylium dye having the formula:

R G) R wherein:

R and R, are aryl radicals selected from the group consisting of phenyl and substituted phenyl having at least one substituent selected from the group consisting of an alkyl radical of from 1 to 6 carbon atoms and an allroxy radical of from 1 to 6 carbon atoms;

R is an alkylamino-substituted phenyl radical having from 1 to 6 carbon atoms in the alkyl moiety;

X is selected from the group consisting of sulfur and oxygen; and

Z- is an anion;

and a carbonate polymer containing the following recurring unit:

wherein:

R is a phenylene radical and each of R and R when taken separately, is selected from the group consisting of a hydrogen atom, an alkyl radical of from 1 to 10 carbon atoms and a phenyl radical and R and R when taken together, are the carbon atoms necessary to form a cyclic hydrocarbon radical, the total number of carbon atoms in R and R being up to 19;

said polymer being in a concentration of about 5 to about 20% of the solution and said dye being in a concentration of about 0.5 to about 20% based on the weight of said polymer, subjecting said solution to shearing for an interval of time of at least about 10 minutes, preparing a second solution of pyrylium dye alone in a concentration of about 0.1 to about g./l., adding said sheared first solution and said second solution to a combination of an organic photoconductor and a polymeric binder difierent from said carbonate polymer, mixing, coating the resultant composition and drying to form a heterogeneous photoconductive composition having a discontinuous phase comprising a co-crystalline complex of said dye and carbonate polymer.

6. The method as described in claim 5 wherein said carbonate polymer is present in the coating composition an amount of about 1 to about 15% and wherein the total solids concentration is between about 2.5 to about 40% by weight of the composition prior to coating.

, m nmnaw sisting of a polyarylalkane having the 'formula:

h 3 t q jp Whitd? t polymeric binder is selected from-the-group consisting of ly("viii'yl'- m-bromobenzoate'-co-vinyl acetate) p yw yl ty poIyIv'inYIEhloride-co-vinyIidenechloride) chlorinated polyethylene, ri is i -t fi 6 m chlorinated polytvinyl ehloride); 1m poly(isopropylidene-bisphenoxyethyl-cqeth lene poly(isopropylidenebisphenoxyethylcoethylene isophtlialatefi .1--- J- cellulose triacetate,

polysulfcne,

polyphenylene oxide and mixtures thereof.

photoconductor and bind er are the same.

1 9. The method as described in claim 5 wherein said organic photoconductor is selected from the group con- 8. The method as described claim 5 wherein said 20 it m -i rbfip a gii s w ad sauiis'al md fidn'rtlie group consisting or hydrogen 'atomlfa'n'falkyl and an aryl.-radical,- at-leastone of D; "Eand G i an ammo s'ubstituen't; a Groupi llli z torganometallic compound having atleast one aminoaryl radical attached to a Group IIIa metal; a Group IYd' qr'gaLfiometallic compound having at least one m eaiynaaan 35 attached to a Group lVa metal; a erosive organemetallic compound haying at least one .aminoaryl- 'radical attached to a Group Va metal; and a polyaryla'mine.

10. A method of forming an electrophotographic element comprising the steps of preparing a first solution of to t about 5 to about 20% of a hydrophobic carbonate polymer containing the following recurring unit:

Li; (pi--01 L l. .I

wherein:

g kisaphenyleneradicalandl. T .i. 5 ach iy keiwhc en s pa at ly; lect of from 1. to: 10 carbonuatornsfland a phenyl radical and R; when taken together, are the carbon atoms necessarytoform a 'cycIic hy- 74 ,drt r o -tra i l, t e lQtal numb r at carbon atoms in-lgandR, being upto19;

20 and about 9.5 :toabout 20% 1 based on the weight-of the P y Of a pyrylium dye having-the formula: v

where n; H t V r ms #9? consisting of phenyl and substituted'phenyl having h. watlgast uqailhstimsn f:sele tedgfr m thegrgupson:

sisting of an alkyl radical of from 1 to 6 carbon atoms an alkoxy radical ofjfrom l to6 carbou atoms? I f R5 isan alkylamino-subs't tuted"phenyl"'radical froni=l to 6 carbon atoms in the alkyl moiety; L; X is selected fromltheg'roup consisting ot sulfur and oxygen; and

isananion:

interval of "time of atleast about 10' minutes, preparing fa second solution consisting essentially of an organio'sol- Win and a t i fiv 'li as the I9a!s!a, I.I .ab9!=, wafayesernii sieasrma concentration of about 0.1-.{0 abs! .19Q..s v .-.L9;a iains t s she re s lut qniand the second solutiortwith anorganic 1 photoconductive material containing a polymer dilferent from said carbonate 'polyiner, mixing the resultant combination, coating a thin film of the resultant composition onto anelectrically cone duct-ive support and drying the film to form a sensitized hs s ogen p o o ondw tiv 'com fion, containing a co-crystalline complex of saidpyrylium dye and car- Fdnhf p ym t c :References'Clted V 1 I UNITEDSTAIES PATENTS q 'sQ i 4 i 1 2 13,110,591; 11/1963 ,;from the groupaconsisting of a hydrogen atom, an M F? ??f 

